Diabetes refers to a disease process derived from multiple causative factors and characterized by elevated levels of plasma glucose or hyperglycemia in the fasting state or after administration of glucose during an oral glucose tolerance test. Persistent or uncontrolled hyperglycemia is associated with increased and premature morbidity and mortality. Often abnormal glucose homeostasis is associated both directly and indirectly with alterations of the lipid, lipoprotein and apolipoprotein metabolism and other metabolic and hemodynamic disease. Therefore patients with Type 2 diabetes mellitus are at especially increased risk of macrovascular and microvascular complications, including coronary heart disease, stroke, peripheral vascular disease, hypertension, nephropathy, neuropathy, and retinopathy. Therefore, therapeutical control of glucose homeostasis, lipid metabolism and hypertension are critically important in the clinical management and treatment of diabetes mellitus.
There are two generally recognized forms of diabetes. In Type 1 diabetes, or insulin-dependent diabetes mellitus (IDDM), patients produce little or no insulin, the hormone which regulates glucose utilization. In Type 2 diabetes, or noninsulin dependent diabetes mellitus (NIDDM), patients often have plasma insulin levels that are the same or even elevated compared to nondiabetic subjects; however, these patients have developed a resistance to the insulin stimulating effect on glucose and lipid metabolism in the main insulin-sensitive tissues, which are muscle, liver and adipose tissues, and the plasma insulin levels, while elevated, are insufficient to overcome the pronounced insulin resistance.
Insulin resistance is not primarily due to a diminished number of insulin receptors but to a post-insulin receptor binding defect that is not yet understood. This resistance to insulin responsiveness results in insufficient insulin activation of glucose uptake, oxidation and storage in muscle and inadequate insulin repression of lipolysis in adipose tissue and of glucose production and secretion in the liver.
Compounds that are inhibitors of the dipeptidyl peptidase-IV (“DPP-4”) enzyme have also been found useful for the treatment of diabetes, particularly Type 2 diabetes [See WO 97/40832; WO 98/19998; U.S. Pat. Nos. 5,939,560; 6,303,661; 6,699,871; 6,166,063; Bioorg. Med. Chem. Lett., 6: 1163-1166 (1996); Bioorg. Med. Chem. Lett., 6: 2745-2748 (1996); D. J. Drucker in Exp. Opin. Invest. Drugs, 12: 87-100 (2003); K. Augustyns, et al., Exp. Opin. Ther. Patents, 13: 499-510 (2003); Ann E. Weber, J. Med. Chem., 47: 4135-4141 (2004); J. J. Holst, Exp. Opin. Emerg. Drugs, 9: 155-166 (2004); D. Kim, et al., J. Med. Chem., 48: 141-151 (2005); K. Augustyns, Exp. Opin. Ther. Patents, 15: 1387-1407 (2005); H.-U. Demuth in Biochim. Biophys. Acta, 1751: 33-44 (2005); and R. Mentlein, Exp. Opin. Invest. Drugs, 14: 57-64 (2005).
Additional patent publications that disclose DPP-4 inhibitors useful for the treatment of diabetes are the following: WO 2006/009886 (26 Jan. 2006); WO 2006/039325 (13 Apr. 2006); WO 2006/058064 (1 Jun. 2006); WO 2006/127530 (30 Nov. 2006); WO 2007/024993 (1 Mar. 2007); WO 2007/070434 (21 Jun. 2007); WO 2007/087231 (2 Aug. 2007); WO 07/097931 (30 Aug. 2007); WO 07/126745 (8 Nov. 2007); WO 07/136603 (29 Nov. 2007); WO 08/060488 (22 May 2008); WO2009025784; WO2010056708; WO2011037793; WO2011028455 and WO2011146358.
The usefulness of DPP-4 inhibitors in the treatment of Type 2 diabetes is based on the fact that DPP-4 in vivo readily inactivates glucagon like peptide-1 (GLP-1) and gastric inhibitory peptide (GIP). GLP-1 and GIP are incretins and are produced when food is consumed. The incretins stimulate production of insulin. Inhibition of DPP-4 leads to decreased inactivation of the incretins, and this in turn results in increased effectiveness of the incretins in stimulating production of insulin by the pancreas. DPP-4 inhibition therefore results in an increased level of serum insulin. Advantageously, since the incretins are produced by the body only when food is consumed, DPP-4 inhibition is not expected to increase the level of insulin at inappropriate times, such as between meals, which can lead to excessively low blood sugar (hypoglycemia) Inhibition of DPP-4 is therefore expected to increase insulin without increasing the risk of hypoglycemia, which is a dangerous side effect associated with the use of insulin secretagogues.
DPP-4 inhibitors also have other therapeutic utilities, as discussed herein. New compounds are needed so that improved DPP-4 inhibitors can be found for the treatment of diabetes and potentially other diseases and conditions. In particular, there is a need for DPP-4 inhibitors that are selective over other members of the family of serine peptidases that includes quiescent cell proline dipeptidase (QPP), DPP8, and DPP9 [see G. Lankas, et al., “Dipeptidyl Peptidase-IV Inhibition for the Treatment of Type 2 Diabetes: Potential Importance of Selectivity Over Dipeptidyl Peptidases 8 and 9,” Diabetes, 54: 2988-2994 (2005); N. S. Kang, et al., “Docking-based 3D-QSAR study for selectivity of DPP4, DPP8, and DPP9 inhibitors,” Bioorg. Med. Chem. Lett., 17: 3716-3721 (2007)].
The therapeutic potential of DPP-4 inhibitors for the treatment of Type 2 diabetes is discussed by (i) D. J. Drucker, Exp. Opin. Invest. Drugs, 12: 87-100 (2003); (ii) K. Augustyns, et al., Exp. Opin. Ther. Patents, 13: 499-510 (2003); (iii) J. J. Holst, Exp. Opin. Emerg. Drugs, 9: 155-166 (2004); (iv) H.-U. Demuth, et al., Biochim. Biophys. Acta, 1751: 33-44 (2005); (v) R. Mentlein, Exp. Opin. Invest. Drugs, 14: 57-64 (2005); (vi) K. Augustyns, “Inhibitors of proline-specific dipeptidyl peptidases: DPP IV inhibitors as a novel approach for the treatment of Type 2 diabetes,” Exp. Opin. Ther. Patents, 15: 1387-1407 (2005); (vii) D. J. Drucker and M. A. Nauck, “The incretin system: GLP-1 receptor agonists and dipeptidyl peptidase-4 inhibitors in Type 2 diabetes,” The Lancet, 368: 1696-1705 (2006); (viii) T. W. von Geldern and J. M. Trevillyan, ”“The Next Big Thing” in Diabetes: Clinical Progress on DPP-IV Inhibitors,” Drug Dev. Res., 67: 627-642 (2006); (ix) B. D. Green et al., “Inhibition of dipeptidyl peptidase IV activity as a therapy of Type 2 diabetes,” Exp. Opin. Emerging Drugs, 11: 525-539 (2006); (x) J. J. Holst and C. F. Deacon, “New Horizons in Diabetes Therapy,” Immun., Endoc. & Metab. Agents in Med. Chem., 7: 49-55 (2007); (xi) R. K. Campbell, “Rationale for Dipeptidyl Peptidase 4 Inhibitors: a New Class of Oral Agents for the Treatment of Type 2 Diabetes Mellitus,” Ann. Pharmacother., 41: 51-60 (2007); (xii) Z. Pei, “From the bench to the bedside: Dipeptidyl peptidase IV inhibitors, a new class of oral antihyperglycemic agents,” Curr. Opin. Drug Discovery Development, 11: 512-532 (2008); and (xiii) J. J. Holst, et al., “Glucagon-like peptide-1, glucose homeostasis, and diabetes, Trends in Molecular Medicine, 14: 161-168 (2008). Specific DPP-4 inhibitors either already approved or under clinical investigation for the treatment of Type 2 diabetes include sitagliptin, vildagliptin, saxagliptin, alogliptin, carmegliptin, melogliptin, and dutogliptin.